Although neuroscientists argue about the degree to which different parts of the brain perform specialist functions, it is known and widely accepted that some specialisation exists.
As far back as the age of Hippocrates (460-370 BC), physicians knew that the brain consisted of two halves. They believed that the left side was the essential half but that the right side was a defunct throwback to some bygone era of human development. In the 1860s the French neurologist Paul Broca discovered that a portion of the left hemisphere controlled the ability to speak language and a decade later a German neurologist made a similar discovery regarding our ability to understand language.

The breakthrough in understanding the right hemisphere came in the 1960s when Roger Sperry discovered that, far from being defunct, the right hemisphere of the brain simply processed information in a different way: Where the left side processed information sequentially, the right side processed it in a more relational way; where the left side recognises a person's name, the right side recognises their face; where the left side is good at logic and analysis, the right side reasons holistically, recognises patterns and interprets emotions and non-verbal expressions.

Also in the 1960s, the neurologist Paul MacLean was looking at the evolution of the human brain. He concluded that our skulls hold not one brain, but three, each representing a distinct evolutionary layer that has formed upon the older layer before it.

The idea that these three brains are somehow separate is now regarded as being incorrect, but it is interesting how the notion of three levels of consciousness also exists in some ancient spiritual traditions. Gurdjieff for example referred to Man as a "three-brained being"; there was one brain for the spirit, one for the soul, and one for the body. Similar ideas can be found in Kabbalah, in Platonism and elsewhere, with the association spirit - head (the actual brain), soul - heart, and body.

More recently fMRI scanning technology has enabled neuroscientists to realise that although the brain unquestionably contains regions that are specialised for processing certain types of information, multiple parts of the brain are involved in virtually everything we do. This breakthrough has enabled us to realise that our thoughts and character are determined less by the brain regions themselves, but more by the relative strengths of the neural networks that connect them.

Prior to these breakthroughs in understanding, profiling tools that related our thinking preferences or personalities to the workings of the brain relied on metaphorical models. Today, based on the latest research, MyBrain International has been able to create the first unifying theory to explain the link between physiology and psychology.